Methyl ester sulfonate (MES) is considered as an efficient and novel surfactant used as main active ingredient in cleansing products. MES is often produced via sulfonation of methyl ester (ME) with sulfonating agent. In this study, ME was synthesized from used cooking oil (UCO) via transesterification and then sulfonated to produce MES using two different sulfonating agents (chlorosulfonic acid (CSA) and sodium bisulfite (NaHSO3)). The influence of various factors (temperature, sulfonating agent/ME molar ratio and time) on MES yield was investigated. Analysis of optimal MES samples was carried out using different techniques (GC-FID, FTIR and 1H NMR). The maximum MES yield of 88.2 % was achieved with CSA/ME molar ratio of 1.2:1 at 70 °C for 3 h while the highest MES yield of 79.4 % was obtained with NaHSO3/ME molar ratio of 1.2:1 at 90 °C for 3 h. FTIR and 1H NMR analyses revealed the presence of methyl (CH2− asymmetric and CH2− symmetric stretching vibrations), esters (C=O, C–O, and O–CH3), and sulfonate (S=O) groups in MESCSA and MESNaHSO3 samples, thereby affirming the desired product. Surface tension analysis showed that the MESCSA and MESNaHSO3 have low critical micelle concentrations of 0.079 g/L and 0.14 g/L, respectively while the corresponding surface tensions were 51.9 mN/m and 30.94 mN/m for MESCSA and MESNaHSO3 respectively.

Developing a robust and facile process route for fatty acid methyl ester sulfonate (MES) synthesis is of importance for industrial applications. Herein, Taguchi orthogonal array (OA) approach was used for the first time to establish the optimum process condition for the sulfonation of methyl esters (ME) with chlorosulfonic acid (CSA). According to the experimental design, the most significant parameter was sulfonation temperature, followed by CSA/ME molar ratio. Under the optimum sulfonation conditions (that is, 70°C sulfonation temperature, 2.0 h sulfonation time, 1.5:1 mol/mol CSA/ME molar ratio and 2.0 h aging time), the MES yield and the corresponding signal/noise ratio were 92.08 ± 0.28% and 39.28, respectively. The obtained FTIR and 1H NMR data revealed spectra associated with methyl (CH2 asymmetric and CH2 symmetric stretching vibrations), esters (CO, CO, and OCH3), and sulfonate (SO) groups in the MES sample synthesized under optimal conditions, thus confirming the target MES product. Surface tension measurements revealed that the optimal MES sample had a low critical miscelle concentration of 0.082 g/L at a surface tension of 51.2 mN/m, implying the possibility of better performance.